Low noack volatility poly alpha-olefins

ABSTRACT

The present invention relates to poly α-olefins (PAO&#39;s) which exhibit superior Noack volatility at low pour points. Mixtures of 1-decene and 1-dodecene are polymerized using an alcohol promoted BF 3  in conjunction with a combination of cocatalysts. The reaction mixture is distilled to remove the unreacted monomeric and dimeric species. The resulting product is then hydrogenated to saturate the oliogomers to provide a hydrogenated product which has a viscosity of 5 cSt. This product is distilled to provide PAO&#39;s of varying viscosity grades. The 4 cSt PAO is comprised mostly of trimers and tetramers while the 6 cSt product is comprised of trimers, tetramers, and pentamers.

FIELD OF THE INVENTION

This invention belongs to the field of lubricants. More particularly,this invention relates to certain improved poly α-olefins prepared froma mixed feed of olefins.

BACKGROUND OF THE INVENTION

Poly α-olefins comprise one class of hydrocarbon lubricants which hasachieved importance in the lubricating oil market. These materials aretypically produced by the polymerization of α-olefins typically rangingfrom 1-octene to 1-dodecene, with 1-decene being a preferred material,although polymers of lower olefins such as ethylene and propylene mayalso be used, including copolymers of ethylene with higher olefins, asdescribed in U.S. Pat. No. 4,956,122 and the patents referred totherein. The poly α-olefin (PAO) products may be obtained with a widerange of viscosities varying from highly mobile fluids of about 2 cSt at100° C. to higher molecular weight, viscous materials which haveviscosities exceeding 100 cSt at 100° C. The PAO's may be produced bythe polymerization of olefin feed in the presence of a catalyst such asAlCl₃, BF₃, or BF₃ complexes. Processes for the production of PAOlubricants are disclosed, for example, in the following patents: U.S.Pat. Nos. 3,382,291; 4,172,855; 3,742,082; 3,780,128; 3,149,178; and4,956,122. The PAO lubricants are also discussed in LubricationFundamentals, J. G. Wills, Marcel Dekker Inc., (New York, 1980).Subsequent to the polymerization, the lubricant range products arehydrogenated in order to reduce the residual unsaturation. In the courseof this reaction, the amount of unsaturation is generally reduced bygreater than 90%.

A major trend in passenger car engine oil usage is the extension of oildrain intervals. Thus, a need exists for low viscosity PAO's whichexhibit low Noack volatility. (See ASTM D 5800 Standard Test Method forEvaporation Loss of Lubricating Oils by the Noack Method.)

The properties of a particular grade of PAO are greatly dependent on theα-olefin used to make that product. In general, the higher the carbonnumber of the α-olefin, the lower the Noack volatility and the higherthe pour point of the product.

PAO's having a viscosity of 4 cSt are typically made from 1-decene andhave a Noack volatility of 13-14% and pour point of <−60° C. PAO'shaving a viscosity of 6 cSt are typically prepared from 1-decene or ablend of α-olefins and have a Noack volatility of about 7.0% and pourpoint of about −60° C.

SUMMARY OF THE INVENTION

The present invention relates to poly α-olefins (PAO's) which exhibitsuperior Noack volatility, while maintaining good low temperatureproperties. Mixtures of 1-decene and 1-dodecene are polymerized usingBF₃ promoted alcohol/ester mixture. The reaction mixture is distilled toremove the unreacted monomeric and dimeric species. The resultingproduct is hydrogenated to saturate the oligomers, to provide a producthaving a viscosity of 5 cSt. This product is distilled and distillationcuts blended to provide PAO's of varying viscosity grades. The 4 cSt PAOis comprised mostly of trimers and tetramers while the 6 cSt iscomprised of trimers, tetramers, and pentamers.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention provides a process for preparing alubricant, which comprises

-   -   (a) oligomerizing an α-olefin feed, wherein said feed is        comprised of 50 to 80 weight percent of 1-decene and 50 to 20        weight percent of 1-dodecene, in the presence of BF₃ and at        least two different cocatalysts, wherein said cocatalysts are        selected from groups (i) and (ii):        -   (i) alcohols and        -   (ii) alkyl acetates,            provided that at least one cocatalyst is from group (i) and            at least one cocatalyst is from group (ii); followed by    -   (b) hydrogenation of at least a portion of residual        unsaturation.

In the above process, it is preferred that the α-olefin feed consistsessentially of 50 to 80 weight percent of 1-decene and 50 to 20 weightpercent of 1-dodecene, with 55 to 75 weight percent of 1-decene and 45to 25 weight percent of 1-dodecene being more preferred. We have foundthat a combination of cocatalysts (or promoters), one cocatalystselected from the class of alcohols, i.e., compounds having one hydroxylfunctional group, preferably C₁-C₁₀ alcohols, more preferably C₁-C₆alcohols, and at least one cocatalyst selected from alkyl acetates,preferably C₁-C₁₀ alkyl acetates, more preferably C₁-C₆ alkyl acetates,provides oligomers which possess desired distributions and physicalproperties. In this regard, we have found that PAO's prepared fromeither group (i) or (ii) alone exhibit low product yields.

In this process, it is preferred that the ratio of the group (i)cocatalysts to group (ii) cocatalysts range from about 0.2 to 15, (i.e.,(i): (ii)) with 0.5 to 7 being preferred.

Preferred C₁-C₆ alcohols include methanol, ethanol, n-propanol,n-butanol, n-pentanol, and n-hexanol.

Preferred C₁-C₆ alkyl acetates include methyl acetate, ethyl acetate,n-propyl acetate, n-butyl acetate, and the like.

We have found that, surprisingly, the products of this process possess agood balance of properties, especially low Noack volatility and pourpoint. Thus, in a preferred embodiment, the present invention provides alubricant which possesses a Noack volatility of about 4 to 12% weightloss, alternatively 6 to 10% weight loss, as determined by a modifiedASTM D5800 method, and a pour point of about −40° C. to −65° C.,alternatively −50° to −58° C., as determined by a modified ASTM D5950method;

-   -   wherein said modified ASTM D5800 method is an ASTM D5800 method        with the exception that thermometer calibration is performed        annually;    -   and wherein said modified ASTM D5950 method is an ASTM D5950        method with the exception that the sample to be tested is not        heated prior to performing said method.

In this regard, the modified ASTM D5800 method is the same as the ASTMD5800 method, with the exception that the thermometer calibration isperformed annually rather than biannually. The modified ASTM D5950method is the same as the ASTM D5950 method with the exception that thesample to be tested is not heated prior to performing said method. Inparticular, the preliminary preheat of the test specimen, as set forthin 11.3.1 and 11.3.2, in ASTM D 5950, is not followed.

The oligomerized α-olefins of the present invention are preferablysubjected to hydrogenation using conventional hydrogenation methodologyto reduce at least a portion of the residual unsaturation which remainsafter the oligomerization. In this regard, typical hydrogenationcatalysts such as Pd, Pt, Ni, etc., can be utilized. In thehydrogenation step, it is preferred that at least about 90% of theresidual unsaturation be reduced. The lubricants thus provided may beutilized as is in lubricant applications or may be formulated with otherconventional lubricants. Accordingly, in another aspect, the presentinvention provides a lubricant composition comprising

-   -   (a) a conventional lubricant; and    -   (b) at least one lubricant comprised of an oligomerized α-olefin        which has been subjected to hydrogenation, wherein said        oligomerized α-olefin is prepared from an olefin feed comprised        of 50 to 80 weight percent of 1-decene and 50 to 20 weight        percent 1-dodecene, wherein said oligomerized α-olefin exhibits        a Noack volatility of about 4 to 12% weight loss, as determined        by as determined by a modified ASTM D5800 method, and a pour        point of about −40° C. to −65° C. as determined by a modified        ASTM D5950 method;    -   wherein said modified ASTM D5800 method is an ASTM D5800 method        with the exception that thermometer calibration is performed        annually;    -   and wherein said modified ASTM D5950 method is an ASTM D5950        method with the exception that the lubricant to be tested is not        heated prior to performing said method.

In the above lubricant compositions, suitable conventional lubricantsinclude known synthetic and natural lubricants which may form a major orminor portion of the overall lubricant composition and their choice andquantity can be tailored to meet desired end-use criteria. (See, forexample, Synthetic Lubricants and High-Performance Functional Fluids,Ed. Ronald L. Shubkin, Marcel Dekker, Inc., (New York, 1993).

The oligomerization reaction can be conducted in a single or multiplestage process to produce a mixture of dimer, trimer, tetramer, andpentamer products. As is shown below in the experimental section, theproduct of the oligomerization reaction is desirably subjected tofractional distillation to afford products via blending having 4, 5, and6 cSt.

Boron trifluoride is used as the catalyst in the process of the presentinvention along with a combination of cocatalysts. As noted above, wehave found that surprisingly, when one selects at least one catalystfrom the classes of alcohols and at least one selected from alkylacetates, followed by conventional hydrogenation, a lubricant having asuperior balance of properties results. The cocatalyst complexes withthe boron trifluoride to form a coordination compound which iscatalytically active. In a preferred embodiment, the cocatalyst is usedin an amount of from about 0.01 to about 10 weight percent, based on theweight of the α-olefin feed, most preferably about 0.1 to 6 weightpercent.

As to the boron trifluoride, it is preferred that it be introduced intothe reactor simultaneously with cocatalysts and olefin feed. It isfurther preferred that the reaction zone contains an excess of borontrifluoride, which is governed by the pressure and partial pressure ofthe boron trifluoride. In this regard, it is preferred that the borontrifluoride be maintained in the reaction zone at a pressure of about 2to about 500 psig, preferably about 2 to 50 psig. Alternatively, theboron trifluoride can be sparged into the reaction mixture, along withother known methods for introducing the boron trifluoride to thereaction zone.

Suitable temperatures for the reaction are also conventional and canvary from about −20° C. to about 90° C., with a range of about 15° to70° C. being preferred.

Further details regarding suitable conventional processing methodologiescan be found in U.S. Pat. No. 4,045,507, incorporated herein byreference, and in Synthetic Lubricants and High-Performance FunctionalFluids, Ed. Ronald L. Shubkin, Marcel Dekker, Inc., (New York, 1993).

Experimental Section

Example 1

A 1-decene and 1-dodecene mixture containing 70 weight percent 1-deceneand 30 weight percent 1-dodecene was oligomerized in two continuousstirred-tank reactors in series at 18° C. and 5 psig using BF₃ promotedwith a 12:1 mole ratio mixture of ethanol and ethyl acetate at a totalcatalyst concentration of 3.5 weight percent. When a steady-statecondition was attained, a sample was distilled to remove the monomersand dimers. The bottoms stream was hydrogenated to saturate thetrimers/oligomers. The hydrogenated product is 5 cSt PAO. A sample ofthis hydrogenated product was distilled and distillation cuts blended toproduce different viscosities of PAO. The 4 cSt PAO contained mostlytrimers and tetramers while the 6 cSt PAO trimers, tetramers, andpentamers. The properties of the final 4 cSt, 5 cSt and 6 cSt PAOproducts as well as those of the 1-decene and 1-dodecene basedreferences are shown in Tables 1, 2, and 3 below. The Noack volatilityof each product is significantly lower than that of the C₁₀ basedreference oil. However, the pour points are higher than those of thecorresponding C₁₀-based reference oils but are well within desiredspecifications. Both the 1-dodecene based 5 cSt and 6 cSt PAO's havepour points that do not meet desired specifications.

EXAMPLE 2

Similar to Example 1, except that the olefin mixture contained 60 weightpercent 1-decene and 40 weight percent 1-dodecene was oligomerized usingBF₃ promoted with a 3.5:1 mole ratio mixture of butanol and n-butylacetate, at a total catalyst concentration of 5.3 weight percent. Withthe incorporation of more 1-dodecene in the feed mixture, the Noackvolatility of each product was further reduced. The pour points areeither the same or higher than those of the products made from 70/301-decene/1-dodecene mix.

EXAMPLE 3

Similar to Example 1, except that the olefin mixture contained 50 weightpercent 1-decene and 50 weight percent 1-dodecene was oligomerized usingBF₃ promoted with a 4:1 mole ratio mixture of n-butanol and n-butylacetate at a total catalyst concentration of 1.8 weight percent. Again,the Noack volatility of each product decreased with the increase of1-dodecene content of the feed mixture. TABLE 1 Properties of 4cSt PAOFeed Pour C₁₀: 100° C. −40° C. Noack Point Example No. C₁₂ Vis. CSt Vis.cSt VI Vol. wt % ° C. Reference A 100:0  4.10 2850 122 13.5 <−60 1 70:304.10 2899 128 11.7 −60 2 60:40 4.09 2680 130 10.6 −60 3 50:50 4.15 2930134 9.9 —

TABLE 2 Properties of 5cSt PAO Feed Pour C₁₀: 100° C. −40° C. NoackPoint Example No. C₁₂ Vis. CSt Vis cSt VI Vol. wt % ° C. Reference B100:0  5.05 4911 135 8.9 <−56 1 70:30 5.10 5272 136 7.7 −56 2 60:40 5.004520 139 7.5 −54 3 50:50 5.00 4346 140 6.4 — Reference C  0:100 5.254647 148 4.8 −45

TABLE 3 Properties of 6 cSt PAO Feed Pour C₁₀: 100° C. −40° C. NoackPoint Example No. C₁₂ Vis. CSt Vis cSt VI Vol. wt % ° C. Reference D100:0  5.9 7906 138 6.8 −59 1 70:30 5.89 7817 140 5.3 −56 2 60:40 5.907400 140 5.0 −54 3 50:50 5.86 6607 143 4.3 — Reference E  0:100 6.208150 146 4.0 −42

While the invention has been described and illustrated with reference tocertain preferred embodiments thereof, those skilled in the art willappreciate that various changes, modifications and substitutions can bemade therein without departing from the spirit and scope of theinvention.

1. A process for preparing a lubricant, which comprises (a)oligomerizing an α-olefin feed, wherein said feed is comprised of 50 to80 weight percent of 1-decene and 50 to 20 weight percent of 1-dodecene,in the presence of BF₃ and at least two different cocatalysts, whereinsaid cocatalysts are selected from groups (i) and (ii): (i) alcohols and(ii) alkyl acetates, provided that at least one cocatalyst is from group(i) and at least one cocatalyst is from group (ii); followed by (b)hydrogenation of at least a portion of residual unsaturation.
 2. Theprocess of claim 1, wherein groups (i) and (ii) are selected from C₁-C₁₀alcohols and C₁-C₁₀ alkyl acetates.
 3. The process of claim 1, whereingroups (i) and/or (ii) are selected from C₁-C₆ alcohols and C₁-C₆ alkylacetates.
 4. The process of claim 1, wherein the C₁-C₁₀ alcohols areselected from ethanol, n-propanol, n-butanol, n-pentanol, and n-hexanol.5. The process of claim 1, wherein the cocatalyst is comprised ofethanol and ethyl acetate.
 6. The process of claim 1, wherein thecocatalyst is comprised of n-butanol and n-butyl acetate.
 7. The processof claim 1, wherein the lubricant possesses a Noack volatility of about4 to 12% weight loss, as determined by a modified ASTM D5800 method, anda pour point of about −40° C. to −65° C., as determined by a modifiedASTM D5950 method; wherein said modified ASTM D5800 method is an ASTMD5800 method with the exception that thermometer calibration isperformed annually; and wherein said modified ASTM D5950 method is anASTM D5950 method with the exception that the lubricant to be tested isnot heated prior to performing said method.
 8. The process of claim 7,wherein the Noack volatility is 5 to 11% weight loss.
 9. The process ofclaim 7, wherein the pour point is −45° C. to −60° C.
 10. The process ofclaim 1, wherein the feed is comprised of 55 to 75 weight percent of1-decene and 1-dodecene and 45 to 25 weight percent 1-dodecene.
 11. Theprocess of claim 1, further comprising the step of subjecting saidlubricant to distillation to afford a fraction having a viscosity ofabout 4 cSt and/or a fraction having a viscosity of about 6 cSt.
 12. Theprocess of claim 11, wherein the 4 cSt fraction possesses a Noackvolatility of 9 to 15% weight loss.
 13. The process of claim 11, whereinthe 4 cSt fraction exhibits a pour point of −45 C to −65° C.
 14. Theprocess of claim 11, wherein the 6 cSt fraction possesses a Noackvolatility of 3 to 10% weight loss.
 15. The process of claim 11, whereinthe 6 cSt fraction exhibits a pour point of −40° C. to −60° C.
 16. Theprocess of claim 1, wherein the cocatalyst is used in an amount of fromabout 0.01 to about 10 weight percent, based on the weight of theα-olefin feed, and wherein the ratio of the group (i) cocatalyst togroup (ii) cocatalyst ranges from about 0.2 to
 15. 17. A process forpreparing a lubricant, which comprises (a) oligomerizing an α-olefinfeed, wherein said feed consists essentially of about 50 to 80 weightpercent of 1-decene and 1-dodecene and 50 to 20 weight percent1-dodecene, in the presence of BF₃ and at least two differentcocatalysts, wherein said cocatalysts are selected from the groups (i)and (ii): (i) alcohols and (ii) alkyl acetates, provided that at leastone cocatalyst is from group (i) and at least one cocatalyst is fromgroup (ii); followed by (b) hydrogenation of at least a portion ofresidual unsaturation.
 18. The process of claim 17, wherein at least 90percent of residual unsaturation is hydrogenated.
 19. The process ofclaim 17, wherein groups (i) and (ii) are selected from C₁-C₁₀ alcoholsand C₁-C₁₀ alkyl acetates.
 20. The process of claim 17, wherein groups(i) and (ii) are selected from C₁-C₆ alcohols and C₁-C₆ alkyl acetates.21. The process of claim 17, wherein the C₁-C₆ alcohols are selectedfrom ethanol, n-propanol, n-butanol, n-pentanol, and n-hexanol.
 22. Theprocess of claim 17, wherein the cocatalyst is comprised of ethanol andethyl acetate.
 23. The process of claim 17, wherein the cocatalyst iscomprised of n-butanol and n-butyl acetate.
 24. The process of claim 17,wherein the lubricant possesses a Noack volatility of about 6 to 10%weight loss, as determined by a modified ASTM D5800 method, and a pourpoint of about −50° C. to −58°, as determined by a modified ASTM D5950method; wherein said modified ASTM D5800 method is an ASTM D5800 methodwith the exception that thermometer calibration is performed annually;and wherein said modified ASTM D5950 method is an ASTM D5950 method withthe exception that the lubricant to be tested is not heated prior toperforming said method.
 25. The process of claim 17, wherein the feedconsists essentially of 55 to 75 weight percent of 1-decene and1-dodecene and 45 to 25 weight percent 1-dodecene. 26-40. (cancelled)